Liquid crystal polyesters, or those which exhibit optical anisotropy in the melt phase, are well known in the art. Numerous patents describe such polyesters and some are, for example, generally described in the article by W. J. Jackson, Jr. appearing in the British Polymer Journal December 1980 entitled, "Liquid Crystal Polymers IV Liquid Crystalline Aromatic Polyesters".
Some aromatic polyesters exhibit optical anisotropy in the molten state and can be melt spun into crystalline fibers which upon subsequent heat treatment further crystallize and substantially increase in tenacity. Such heat treated polyester fibers can be used for numerous purposes such as, for example, in tire cords and in other industrial and consumer products where high strength and low weight with its attendant economic and other advantages are desired. In addition to their use in the form of fibers, such polyesters can also be formed by molding, for example, injection molding, into a wide variety of substrates which will have outstanding stiffness and toughness and strength. Specific applications for such type liquid crystal polyesters are as high strength reinforcements for numerous thermoplastic and thermosetting polymer materials or as a matrix resin for various molded articles.
In accordance with the present invention, an improved low cost, high performance thermotropic polyester, which is optically anistropic in the melt, is manufactured and processed into usefully shaped articles, as by being formed into fibers or molded into other useful articles using conventional thermoplastic polymer processing and forming technology. The processing includes a step of devolatilizing the polyester after synthesis but prior to subjecting the polyester to conventional shaping operations, such as fiberization or molding, e.g., injection molding, either with or without compounding.
The melt spinnable, liquid crystal polymers contemplated herein are of fiber forming molecular weight and exhibit optical anisotropy in the liquid phase and consist essentially of recurring moieties. ##STR3## and, moiety III or moiety IV wherein ##STR4## wherein the mole ratio of moiety II to moiety III, when present, is 1:4 to 2:1 and wherein the mole ratio of moiety II to moiety IV, when present, is 2:8 to 1:9.